HID light distance ?

Discussion in 'Growing Marijuana Indoors' started by skiweeds, May 22, 2010.

  1. how close can i put my HID light to my plants. im flowering right now with a 400 watt hps bulb. im using the euro reflector from htg supply. the hood is sealed with a piece of glass under the light so the exhaust hooks up to the side and sucks out the hot air. i just thought today, since that piece of glass is trapping a lot of the heat from reaching the plants, can i put them closer than normal? or is the light still too intense or something like that? im not really a newb when it comes to lighting but im also obviously no expert. i read normally to keep then 12 - 18 inches from the light so far i have been doing that. but then i thought about the glass piece and less heat so maybe they can go closer. i just dont want to move them and have the tops get burnt. how much closer can i move them if i even can? does this apply during vegging when i use a 400w mh conversion bulb? is there some certain way you can tell how close you can have it? like can i tell by putting my hand under the light and slowly lower until it feels not as hot? thanks
  2. Bingo, grasshopper. You just answered your own question! ;) Every environment is different but I keep mine generally around 14ish (600w HPS). Once mine quit growing height wise at about 5 1/2 weeks of 12/12 I lock it in to the closest being 12" and leave it there. ;)
  3. The hand rule is a good guide. Here is a better one for light intensity:

    Light Distance Chart's

    The actual power will vary depending on your ballast and bulb but its a useful guide. Too close and the light will bleach the plant and the heat will cause heat stress as plant enzymes have temperature limits. Too far away and you'll be losing out on light power to the plant.

    For heat, I use a temp guage with a probe on a wire. This is the most accurate way I've come up with for measuring the temp at a certain point. Hang the probe on top of the bud closest to the light and see what the temp is there.

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